Cam controlled automatic screw machines are metal working lathes whose automatic operation is obtained by a cam shaft which controls the succession of productive operations and idle periods and the movements of all working parts. The cams on the shaft may be changed or adjusted and, once set, such machines are automatic, producing a series of identical parts from a piece of bar stock.
Traditionally, these machines are limited to performing operations that require the work to be rotating, such rotation being applied by the headstock spindle within which the work is held. In order to perform operations in which the work is stationary, such as cross drilling or the like, it has been necessary to remove the part from the screw machine and take it to another machine for the stationary operation. Alternatively, the spindle rotation must be stopped and the screw machine provided with the necessary tools to perform the stationary operation. Stopping the spindle rotation is necessary to avoid breakage of cross milling tools and drills. Also, it is necessary in some cases to be able to properly position the operation performed by the stationary tool. Furthermore, in the case of fine tolerance parts, the rotary positioning of the work must be accomplished with accuracy so that the site of the stationary operation is precisely located. Applicants' prior U.S. Pat. No. 5,105,925 discloses such a braking attachment for automatic Swiss screw machines.
However, cam controlled automatic screw machines are further limited in that the headstock spindle rotates in only one direction and at one speed for any particular set-up. Since the spindle is normally driven from the main motor of the machine which also drives the cam shaft which controls the operating sequence of the tools, it is not possible to change either the rotational direction of the spindle or its speed during operation as this would also affect the cam shaft rotation and, thereby, the sequence of tool operations. Such capability on existing machines is desireable because of the cost of replacing them with newer models and the deficiencies of the newer machines themselves.
Although newer models of these machines have means for stopping the spindles and changing their direction or speed of rotation built in or available as an additional option, the mechanisms of these devices involve a complex assembly of clutches and bearings within the machines. Such assemblies require the services of an experienced mechanic to set and maintain them and are not adaptable to other types of machines or indeed to the large established base of older machines which are in current and daily use. In addition, because these newer machines still drive the spindle and the tool operations off of the main machine motor which, together with the driven portions of the machine, presents a large mass to stop and start, indexing and changes in the direction of rotation of the spindle on these machines is more difficult to achieve.
Recognizing the need for a simple apparatus, easily adaptable to existing cam controlled automatic screw machines which would add the desired capabilities thereto, the inventors herein have devised such an apparatus, comprising essentially four parts, that is simple to set-up and use yet provides positive and accurate control over the rotation of the screw machine spindle in concert with the tool head operation of the machine. In addition, the apparatus of this invention provides for more economical operation of machines on which it is installed in that it provides faster speeds of operation, including faster rates of indexing, speed and direction changes, in most cases allowing a greater number of parts to be produced in a given amount of time over other machines.